Physiological tissues are typified by specific electrical impedance characteristics. Variance in types of epithelial tissue, for example, may be recognized by differences in electrical characteristics (Gonzales-Correa C A et al., “Virtual biopsies in Barrett's esophagus using an impedance probe”, Annals of NY Academy of Sciences, Vol. 873, April 1999, pp. 313–321).
Changes of this characteristic impedance can provide essential information about the tissue, and the entire organism. This concept has been the springboard for a great deal of research into predicting pathological conditions, especially cancer (Blad B and Baldetorp B, “Impedance spectra of tumor tissue in comparison with normal tissue: a possible clinical application for electrical impedance tomography”, Physiological Measurements, Vol. 17 Suppl 4A, November 1996, pp. 105–115). For example, the early detection of colon cancer may be possible by examining differences in electrical properties of surface colonic epithelium (Davies R J et al., “Colonic epithelial impedance analysis in a murine model of large-bowel cancer”, Archives of Surgery, Vol. 124(4), April 1989, pp. 480–484). These measurements are generally done using an endoscope or a probe with electrodes at the end.
Similarly, breast cancer may be predictable based on impedance differences in normal and pathological tissue (Chauveau N et al., “Ex vivo discrimination between normal and pathological tissues in human breast surgical biopsies using bioimpedance spectroscopy”, Annals of NY Academy of Sciences, Vol. 873, April 1999, pp. 42–50; and Jossinet J, “A Variability of impedivity in normal and pathological breast tissue, Medical and Biological Engineering and Computing, Vol. 34(5), September 1996, pp. 346–350).
Many other conditions may be predictable based on electrical impedance changes. For example, esophagus impedance may be related to Barrett's esophagus, a disorder in which the normal squamous mucosa of the esophagus is replaced by columnar epithelium (Gonzales-Correa C A et al., “Virtual biopsies in Barrett's esophagus using an impedance probe”, Annals of NY Academy of Sciences, Vol. 873, April 1999, pp. 313–321). Changes in oral impedance may be related to changes in oral mucosa (Nicander B L et al., “Electrical impedance. A method to evaluate subtle changes of the human oral mucosa”, European Journal of Oral Science, Vol. 105(6), December 1997, pp. 576–582). Other diagnoses using this principle include tissue injury (Paulsen K D et al., “In vivo electrical impedance spectroscopic monitoring of the progression of radiated-induced tissue injury”, Radiation Research, Vol. 152(1), July 1999, pp. 41–50), lung ventilation (Frerichs I et al., “Monitoring regional lung ventillation by functional electrical impedance tomography during assisted ventillation”, Annals of NY Academy of Sciences, Vol. 873, April 1999, pp. 493–505), and ischemic tissue (Casa O et al., “In vivo and in situ ischemic tissue characterization using electrical impedance spectroscopy”, Annals of NY Academy of Sciences, Vol. 873, April 1999, pp. 51–58).
Measurement of impedance characteristics of tissue is typically accomplished through the use of a probe with electrodes or by implanting electrodes (Lehrer A R et al., “Electrical resistance of genital tissues during reproductive events in cows, and its possible on-farm applications: A review”, Wiener Tierarztliche Monatsschrift, Vol. 78, 1991, pp. 317–322). The electrodes may be attached to the end of an enteroscope for measurements of the intestines. Additional techniques have been developed as well. One of these techniques is termed “electrical impedance tomography”, or EIT (Brown B H et al., “Applied potential tomography: possible clinical applications”, Clinical Physiology and Physiological Measurements, Vol. 6(2), May 1985, pp. 109–121). This method involves resistivity distribution changes following ingestion of conducting or insulating fluids. In addition, body composition may be analyzed by total body conductivity (Galvard H, et al., “Differences in body composition between female geriatric hip fracture patients and healthy controls: body fat is a more important explanatory factor for the fracture than body weight and lean body mass”, Aging (Milano), Vol. 8(24), August 1996, pp. 282–286; and Yasiu T, et al., “Body composition analysis of cachetic rabbits by total body electrical conductivity”, Nutrition and Cancer, Vol. 32(3), 1998, pp. 190–193).